Don,
I used and really liked the Herculiner Bed Liner product - Herculiner Truck Bed Liners. The first coat looked a bit splotchy, but with a second coat it filled in and was very uniform on the bottom of the '33 body. It applies easy, and seems to be tough as nails. Lots of the Jeep/Off-road crowd use it for the inside of tubs that can be easily sprayed out for cleaning.